Telephone trunking system.



l. G. ROBERTS. TELEPHONE TRUNKING SYSTEM.

APPLICATION FILED DEC. 8, |914.

Patented Mar. 13, 1917.

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J. G. ROBERTS. TELEPHONE TRUNKNG SYSTEM. 'APPLICATION mso usc.s.1914.

Patented Mar. 13, 1917.

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JOI-IN G. ROBERTS, OF DOBBS FERRY, YORK, ASSIGNOR, BY MESNE ASSIGNMENTS,T0 WESTERN ELECTRIC CQIVIPANY, IN CORPGRATED, A CORPORATION OF NEW YORK.

TELEPHONE TRUNKING SYSTEM.

Specification of Letters Patent.

Application filed December 8, 1914. Serial No. 876,084.

To all whom it may concern Be it known that I, Jol-IN G. ROBERTS, acitizen of the United States, residing at Dobbs Ferry, in the county ofWestchester and State of New York, have invented certain new and usefulImprovements in Telephone Trunking Systems, of which the following is afull, clear, concise, and exact description.

This invention relates to trunking and telephone exchanges. It isapplicable especially to two-wire trunks between offices, and as soapplied its objects are to effect the control of supervisory signals andother devices over the trunks without the use of controlling circuitsextending through ground or a third wire between the oilices, andpreferably also without the use of marginal controlling devices.

lVhere subscribers lines to be connected terminate in diilierentoltices', it is desirable to provide two-wire interoflice trunks inorder to economize in conductors. It is also desirable where theconnection extends through such aV trunk, to supply talking current tothe calling and called subscribers lines by separate batteries, one ateach oiiice, instead of a single battery as usual where the two linesterminate in the same oliice.

lt is furthermore desirable in providing for the necessary signalingoperations over an interollice trunk, to avoid the use of controllingcircuits which depend upon a ground return path between the otlices,this in view ot' the disturbing effects which sometimes occur in groundcircuits due to diftercnces or variations of ground potential betweenthe otlices. ln certain systems, such as manual multi-office, and alsoin semi-automatic exchanges which provide operators answering equipmentand automatic switches under the control of operators senders forcompleting the connections to wanted lines, it is required that thecalled subscriber shall have control over the trunk of a supervisorysignal at the outgoing end of the trunk, and that the operator shall beable to control at will either the release of the automatic switches atthe incoming end of thetrunk, or the restarting of an automatic ringingequipment without requiring for the latter purpose the restoration ofthe connection and the building of it up again. This invention providesin a telephone exchange system elective means operable over a combinedtelephonie link and controlling circuit and without marginal controllingdevices, for controlling the foregoing or similar operations.

In accordance with another feature of the invention, a differentialrelay for controlling the called supervisory signal is provided for thecalled line end of the operators connecting circuit. When this circuitvis used to form the outgoing end of an interottice trunk, the trunk iswholly free from ground or battery connections, at the outgoing end,battery being supplied to the trunk circuit through one winding of therelay from the incoming' end of the trunk, the other winding beingincluded in a local circuit; but when the connecting circuit is directlyunited to a called line the battery and both windings of thedifferential relay are switched into the circuit, and current issupplied outwardly to the called line. Whenever the connection isestablished through an interoflice trunk, the called line supervisorysignaling device is controlled by reversals of current at the incomingend under control of ka relay controlled in turnl by current in thecalled line. By means of compensating resistances included in thevarious trunk lines at their incoming ends, the total resistances of alltrunks may be made equal, thus reducing to a minimum the current marginsfor controlling the differential relay. Included in the trunk at theincoming end is a relay unaffected versals but responsive to currentinterruptions. This relay remains in the circuit whether the current ison the trunk in one direction or the other, and is available always forcontrol by the operator to effect or to cause the operation of thedisconnect signal or switch restoration.

Itis a' further feature of the invention that this same controllingdevice or relay at the incoming end of the trunk is adapted by specialcontrol from the outgoing end, as by a momentary interruption of currentto ca use rei-inging on the called subscribers line.A

The invention will be more fully understood by reference to theaccompanying drawings. In Figures l, 2 and 3 is shown a.y system ofcircuits suitable for a semiautomatic exchange. Fig. 3 represents a lineto be called that terminates in the same otlice as the calling line.

Patented Manie, 1917.V

by the current rcf the rering Referring first to the semi-automaticcircuits in Figs. 1, 2 and 3, a connection is as sinned to have beenestablished from the calling station 1 to a called station 2 through aninterotlice trunk comprising the` two wires 3 and il. Fig. 3 illustratesa three-wire local trunk extending to a called station, and this trunkitself comprising the talking circuit conductors and G andtliird wire 7.The circuit shown in Figs. 1 and 2 is established by way of a plug andjack switch 9 of an operators connecting circuit, the said connectingcircuit, the two-wire trunk El, al., contacts 11 and 12 of an automaticswitch and contacts 13 and 11 of another automatic switch. Talkingcurrent is supplied to the calling line by battery 15 and to the calledline by a battery 1G. The latter battery also supplies current at theincoming end of the trunk backwardly to the connecting circuit. lllhenthe connection is established, the called subscriber has control over asupervisory signal 17 b means of a supervisory relay 18, one win ing ofwhich is included in the trunk line circuit at the outgoing end. Thiscontrol is effected bythe operation of a battery reversing relay 19 in alocal circuit controlled by the relay 21 in the circuit leading to thecalled line. An automatic ringing apparatus 22 operates, in the firstinstance, automatically to ring the bell at the called subscribersstation 2 and is tripped and the ringingy current disconnected from theline when the called subscriber answers. If the called subscriberanswers and replaces his receiver on the switclihook and the operatordesires to start the automatic ringing apparatus again, she may do so bydepressing key 23 which produces a momentary interruption in the trunkcircuit. This affects relay :24 in such a way as to again place theringing apparatus into active con'd'tion. To cause switch restoration, aprolonged interruption in the trunk circuit at the outgoing end bringsabout the energization of a switch restoring magnet 25.

In case the callinO' subscriber is connected to a line which terminatesin the same office so that a local trunk circuit 5, 6, 7 would be usedinstead of the interoliice trunk circuit 3, 4, there is brought intooperation a switching relay 2G which connects battery in circuit to thecalled line.

The foregoing very briefly states the scheme of operation and functionsof the principal devices in the system. A more detailed description ofthe operation still re ferring to Figs. 1, 2 and 3, is as follows:

The apparatus associated with the operators connecting circuit is inpart controlled by a sequence switch 27, certain of the restingpositions of which as determined by the master contact 28 may be: 11selection,

1lringing, 1G talking, 18 switch restoring. The apparatus associatedwith the inconiing end of the trunk may likewise be controlled in partby sequence switch 29, certain of the resting positions of which asdetermined by its master contact 31 may be; 13 waiting trunk closure, 16talking and 18 switch restoring. The circuits and apparatusnioredirectly involved in the operation of selection and the establishment ofthe circuits up to the point shown in the' diagram, are omitted to avoidconfusion. It is assumed, therefore that the sequence switch 27 hasreached its position 11 and the sequence switch 29 its position f3.Further progress in the operation of the system is then started by theclosingofa contact 32 which is preil'erably effected automatically atthe termination of a selecting operation. This closes a circuit-ground32, 33, 2T, battery, which sends the sequence switch 2TA out of position11 into its ringing position 1l wherein there is closed a circuit forthe ringing lamp 3l as follows: battery 35, 3l, 3G, ground. The functionof this ringing lamp is to indicate to the operator that the ringingoperation has begun and the lamp remains li glitcd until the subscriberanswers. Tn advancing to position 1i, the sequence switch 27 completesat contacts 37 and 38 the trunk line which now forms a combinedtelephonic link and controlling circuit. Relay 2G is not energized atthis time because the third contact 39 of the trunk is free fromconnections to establish a circuit. The trunk circuit as a combinedtelephonic link and controlling circuit may be traced as follows: 1c,ai, ii, 42,13, i, 12, i12, es, il, is, i7, is, 37,117,11, 3, i9, 51, ce,ground. This circuit includes the winding of relay 24C and a. singlewinding i6 of the supervisory control relay 1S. A circuit is also closedfoi' the other winding 52 of relay 18 as follows: l5, 53, 5l, ground.The trunk circuit as traced may include the coinpensating resistances112 and 51, the purpose of which is to render the total resistance ofthe trunk circuit equal to the resistances of other trunk circuits withwhich the supervisory relay 18 may be required to operate. That is tosay, where the trunklines vary in length, the resistances and 51 wouldbe varied so that the total resistances of the lines themselves plusthese compensating resistances would in all trunks be the saine. Theresistance in the circuit of the winding 52 ofthe supervisory relay 18may be provided to cut down the current in this winding. Relay 1S,therefore, has current flowing through windings :elfi and in oppositedirections and of equal magnetizing force, so that the relay is notA atthis time energized.

Upon the energization of relay 2li 1n the trunk circuit there is closeda circuit ground 29, battery, which sends sequence switch 29 out of itsposition 13 into its talking position 16. On entering position 14 andcontinuing to position 16, there is closed a circuit: ground, 56, 58,59, battery, which energizes the slow release relay 59, so that by thetime the sequence switch reaches position 16, relay 59 is energized andits contact 61 is opened. 1n position 16, contacts 62 and 63 are closedwhich completes the path for current to the called line.

lVhen sequence switch 29 left position 14, it opened at contact 64 thecircuit of a holding rela-y 65, resulting in the closing of contact 66to prepare for the operation of the automatic ringing apparatus 22.Relay was energized in position 12 of the sequence switch 29 over acircuit from ground, bat tery, winding of relty 65, the upper contact of64, to ground.` The ringing apparatus becomes active as soon as thesequence switch reaches position 16, in which contact 67 is closed. Thecomplete local ringing' control circuit then closed is as follows:ground, 56, 67, 68, 69, 70, 66, battery. Relay 68 is energized,connecting the generator 71 in circuit with the called line as follows:71, 72, 73, 74, 63, 14, 2, 13, 62, 75, ground. 1V hen the subscriberresponds, the current in the line increases, so that relay 72 which ismarginal, acts, opening at contact a shunt preexisting about relay 76.This relay 7 6 in turn closes at contact 77 a shunt about relay 68 sothat the latter denergizes opening the ringing circuit and closing thebattery circuit to the called line, as follows: 1e, 9.1, so, 40, es,1&1, 2, 1s, 62, 50, 7o, ground. When this circuit is closed, thesupervisory control relay 21 is energized, closing a localcircuit-battery 78, 19, ground, and relay 19 acts to reverse theconnections of the battery 16 to the trunk wires 3 and 4. The rererselyconnected circuit for the battery over the trunk line is as follows: 16,24, 79, a9, a, 11, 117, 37, as, 47, 46, 45, 44, 38, 112, 12, 4, 43, 81,ground. Relay 24 remains in the circuit and is unaffected by thereversal O15-connections, but the direction of current. in winding 46 ofthe superwisory relay 18 is reversed, so that the currents in the twowindings 46 and 52 now assist, and the relay is energized, closing atits contact 83 a circuit-ground 83, 84, 27, battery, which sends thesequence switch 27 out or' its ringing position 14 into its talkingposition 16. In this latter position, the supervisory signal lamp 17 isbrought into a circuit-battery 35, 17, 85, ground, but the lamp isshunted by a path through the resistance 86 by way of contacts 87 and 83to ground.

Repeated openings and closings of the called subscribers line, by thesubscriber replacing and lifting his receiver, will under this conditionof the apparatus result in repeated reversals of current in the winding46 of the supervisory relay 18, thus repeatedly denergizing andenergizing this relay and opening and closing the shunt about thesupervisory lamp signal 17. The called subscriber thus has effectivecontrol over the supervisory signal 17 and, in any condition of thecalled subscribers line whether opened or closed, relay 24 at theincoming end of the trunk remains unaffected in the circuit.

The control of the automatic ringing apparatus 22 to cause reringing onthe called line may be secured by the momentary depression of the reringkey 23. This closes at contact 88 a shunt of contact 44 of relay 89, andat contact 91 a circuit for relay 89. The latter opens contact 44. Thetrunk circuit remains closed, however, at contact 88 until the reringkey 23 is restored. Relay 89 is timed to release a moment after itscircuit is opened, say in one-tenth of a second. The trunk circuit isthus opened momentarily and then closed again at contact 44. This allowsrelay 24 to react momentarily, opening at contact 56 the local ringingcontrol circuit and also the circuit through the slow release relay 59.The interruption in the trunk circuit is of such short duration,however, that relay 59 does not have time to react to close contact 61,but the locking-out relay 76 in the local ringing control circuit doesreact, opens at contact 77 the shunt about the ringing relay 68 andcloses at contact 69 the shunt about itself. Ringing is thus againstarted by the energization of relay 68. If the called subscriberresponds again, the operation of tripping the ringing is repeated, thesupervisory control relay 21 is again energized, relay 19 is againenergized, current from battery 16 is again reversed in the trunkcircuit and the supervisory relay 18 is again energized by the reversalof current in its winding 46, so that the supervisory lamp signal 17again responds.

The control of switch restoring over the trunk line is never taken awayfrom the operator, but may be effected whether the called subscriberstelephone is on or oft' the hook, since relay 24 remains continuously incircuit. The operator may thus cause switch restoration at the incomingend of the trunk at any time by a prolonged opening of the trunk circuitin anysuitable manner. The system shown is so organized that when theoperator opens the circuit of the calling lino at the plug and jackswitch 9 by removing the plug from the jack, the local circuit includingthe cut-ofi3 relay 93 and cord relay 94 is opened. The latter relayopens at its contact 95 the local circuit of the calling supervisorysignal 96 and closes at contact 97 a circuit, ground, 97, 98, 27,battery, which sends sequence switch 27 out ofits talkingY position 16.into its switch restoring position 18, wherein there is closed atcontact 99 the circuit oi a switch restoring magnetlOl. This effects therestoration of the automatic switch which had previously closed thetrunk circuit at contacts 11 and 12. Then this sequence switch leavesposition 16, it opens the trunk circuit at contacts 37 and 38 and relay24 reacts as before. This time however the trunk circuit is not againclosed. Therefore, the slow-release relay 59 has time to react, andcloses at contact 61 a circuit, ground, 61, 102, 29, battery, whichincludes the motor magnet of sequence switch 29, sending it out of itstalking position 16 into its switch restoring position 1S, wherein isclosed at contact 103 a circuit for the switch restoring` magnet 25.This effects the restoration of the automatic switch which hadpreviously closed at contacts 13 and 14 the circuit to the called line.

It the callingsubscribcr had been calling for connection with a`subscribers line terminating in the same oiiice as that at which thecalling line terminates, the connection would be established directly tothat line through a local trunk, such as the three-wire trunk, 5, 6, 7indicated in Fig. 3. The local circuit terminal of conductor 7 in such.a trunk is connected through a resistance 105 to battery, so that whenthe connection is set up to a local trunk, there is established acircuit for the switching relay 26 as follows: ground, 106, 26, 107,10S, 109, 7, 105, battery. In this event the relay 26 changes that partof the connecting circuit which leads toward the called line so thatcurrent is supplied thereto through repeating coil windings and 46 frombattery 15, this circuit being as follows: 15, 52, 111, 46, 45,V

44, as, na, ne, c, iii, s, 115, s, 116, 117, 37, 4S, 11S, ground. Thesupervisory relay 18 now operates as an ordinary .supervisory relayunder the control of the called substation S, its two windings 52 and 46operating cumulatively in the circuit just traced to Y that station.Each of the windings 52 and 46 of the supervisory relay 18 may bepermanently shunted by non-inductive windings 119 and 121 to reduce theimpedance to voice currents. These two shunts may be proportioned withrespect to the two windings in exactly the same manner as the ordinarynon-inductive shunts 122, 123 and 124 of the calling supervisory relay125, the controlling relay 24 and the called line supervisory controlrelay 21 respectively.

'Vhat is claimed is:

1. In a. telephone system, a trunk line forming a combinedtelephoniclink and controlling circuit, a differential signal controlling devicehaving one winding in said circuit at the outgoing end, means forsupplying current to the other winding of said relay, a repeating coil,a source of current connected through the winding oit' said repeatingcoil in the incoming end ot said circuit, and means for repeatedlyreversing the direction of current flow to said outgoingl 2. In atelephone exchange system, a calling subscribers line, a trunk lineforming a combined telephonie link and controlling circuit, means forinductively connecting the controlling circuit to said-line, a localcircuit, a source of current therein, an electromagnetic signalcontrolling device having one winding in said local circuit and a secondwinding in the outgoing end of said controlling circuit, the magnetizingforces exerted by said windings being approximately equal, a source ofcurrent in the incoming end of said controlling circuit, and means forreversing the connections oi said source.

3. In a telephone exchange system, a calling subscriber-s line, a trunkline forming a combined telephonie link and controlling circuit, meansfor inductively connecting the controlling circuit to said line, asignal controlling device responsive to current reversal-s and includedin theoutgoing end of said circuit, a source of current in the incomingend of said circuit, means for reversing the connections ot' saidsource, a controlling device unresponsive to current reversals includedin the incoming end of said circuit and unaffected by current reversalsresponsive-to the openingand closing of said circuit, and a switch forcontrolling said last mentioned device in the outgoing end of saidcircuit.

4. In a telephone exchange system, a connecting circuit, a localcircuit, a source of current, a super `isory controlling magnet havingtwo windings, and means operable at will for including both of saidwindings in said connecting circuit or one and the said battery in saidconnecting circuit and the other in said local circuit.

v5. In a telephone exchange system, trunk line forming a combinedtelephonie link and controlling circuit, a supervisory signal device atthe outgoing end and a ringing device and a disconnecting device at theincoming end of said trunk, the said supervisory signal being responsiveto reversals of current, the said ringing apparatus to a momentaryinterruption of current, and the said disconnecting device to aprolonged interruption of current in said circuit, and means at each endof said trunk for controlling said devices over said circuit.

6. In a telephone exchange system, a calling subscribers line a trunkline forming a combined telephonie link and controlling circuit, meansfor incluctively connecting the controlling circuit to said line, asupervisory device at the outgoing end of said trunk responsive toreversals of current in said circuit, a disconnecting device at theincoming end of said trunk responsive to an interruption of current insaid circuit, and means at each end of said trunk for controlling saiddevices over said circuit.

7. In a telephone exchange system, a telephone line, a trunk lineforming a combined telephoniclink and controlling circuit, means forinductively connecting the controlling circuit to said line, asupervisory relay included in the outgoing end of said trunk responsiveto reversals of current therein, a relay included in the incoming end ofsaid trunk and unresponsive to such reversals of current, two devicescontrollable by the last mentioned relay, one responsive thereto upon amomentary interruption and the other upon a prolonged interruption ofcurrent in said circuit, and means at each end of said Copies of thispatent may be obtained for ve cents each, by addressing the Commissionertrunk for controlling said relays over said circuit.

8. In a telephone exchange system, a two Wire trunk line forming acombined telephonie link and complete controlling circuit, a localcircuit, a source of current therein, an electromagnetic signalcontrolling device having one Winding in said local circuit and a secondWinding in the outgoing end of said controlling circuit, a source ofcurrent in the incoming end of said controlling circuit and means forreversing the connections of said source.

In Witness whereof, I hereunto subscribe my name this 7th day ofDecember A. D., 19

JOHN G. ROBERTS. Vitnesses:

E. Emmen,

F. Fnrsrnn.

0f Patents,

Washington, D. C.

